Selective Laser Trabeculoplasty (SLT)
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SLT is indicated for the treatment of ocular hypertension, primary open angle and secondary open angle glaucomas, such as pseudoexfoliation and pigment dispersion glaucoma. Steroid induced glaucoma is another possible candidate for the procedure. Narrow angle glaucoma, where the trabecular meshwork is not obstructed by iris apposition or synechiae, may also benefit. If there is synechial closure, trabeculoplasty is not advised. Contraindications are inflammatory, iridocorneal endothelial (ICE) syndrome, developmental, and neovascular glaucoma. Laser trabeculoplasty is also not effective in angle recession glaucoma due to distortion of the angle anatomy and TM scarring. If there is a lack of effect in one eye, then it is relatively contraindicated in the fellow eye.
In SLT, the laser is a frequency-doubled (532-nm) Q-switched Nd:YAG laser. The laser settings are fixed except for the power. Spot size is 400-microns and pulse duration is 0.3 ns. The large spot size results in low fluences (mJ/cm2). In more lightly pigmented angles, initial energy can be set at 0.8-1.0 mJ. In more heavily pigmented angles, the initial power can start off lower at 0.3-0.6 mJ. The aiming beam is centered over the trabecular meshwork and straddles the entire TM. The aiming beam will not be in sharp focus when the surgeon focuses on the trabecular meshwork to deliver treatment. The treatment endpoint is the appearance of small cavitation bubbles adjacent to the TM. Generally, 180 or 360 degrees are treated in a session. Laser spots can be placed contiguously or several spot sizes apart.
It is routine to place a drop of apraclonidine or brimonidine in the eye after SLT to decrease the risk of a IOP spike. The follow-up thereafter will depend on the patient and doctor, but a commonly followed routine is 4-6 weeks later for an IOP check and then every 3-4 months depending on the severity of the glaucoma present.
A transient rise in IOP after laser trabeculoplasty is the complication of greatest significance to glaucoma patients undergoing this treatment. Postoperative IOP rise is more severe and frequent with higher energy levels, 360° treatments, posterior placement, heavy angle pigmentation, and a low preoperative outflow facility. Spikes are usually transient, occur within the first hour although they may be delayed, and most resolve with medical treatment by the next day.
In SLT prophylactically treated for a pressure spike, the reported rate of an IOP rise > 5 mmHg is around 10% or less and the rate of an IOP rise > 10 mmHg is around 3%. There are rare cases requiring trabeculectomy for sustained IOP increases after SLT and this possibility should be included in the informed consent process for either procedure. Corneal edema attributable to HSV reactivation has been reported following SLT. The thought is that the inflammatory cascade following laser contributes to virus reactivation. Hyphemas have also been reported, but are rare.